Diffuse reflectivity of visible light is important in many applications. Direct view displays used in electronic equipment (e.g., instrument panels, portable computer screens, liquid crystal displays (LCDs)), whether relying on supplemental lights (e.g., backlight) or ambient light, require diffuse reflectant back surfaces to maximize image quality and intensity. Reflectivity is particularly important with backlit direct view displays in battery powered equipment, where reflectivity improvements directly relate to smaller required light sources and thus lower power demands.
Portable computer LCDs are a substantial and demanding market requiring high levels of diffuse reflection of visible light from very thin materials. For certain markets it is important that the backlight reflector is relatively thin, i.e., less than 250 μm and sometimes less than 150 μm, to minimize the thickness of the completed display.
The reflective material used in LCD backlights has a significant effect on the brightness, uniformity, color and stability of the backlight unit and, ultimately, the LCD module. For a direct view LCD backlight, requirements for the reflector can include high photopic reflectance (e.g., sometimes greater than 95%) and stability under use conditions including cavity temperatures of 50° C. to 70° C., stability to ultraviolet (UV) light from cold cathode fluorescent lamp (CCFL) sources, as well as to humidity and temperature cycling. In direct view backlights, the reflector is an integral part of the backlight unit and, therefore, the physical properties of the material are also important. Requirements for an edgelit backlight differ in that the operating temperature is typically lower and the need for UV stability can be less in instances where there is UV absorption in the light guide. However, additional requirements on edgelit backlight reflectors include the need to make uniform contact with the light guide without damaging it, and minimizing reflector thickness.
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